Unusual lines on UV map after using “Difference” to create apertures on a plane
Using the Boolean to cut the openings left the object with only 2 faces, Filling in these  Concave Ngons caused the lines you see in the UV space. If you enable the face select mode this will become more obvious.



These Ngons will not be a problem as such once the object is imported into SL as the importer will convert those Ngons to triangles.


But as FFeller suggested using loop cuts is a much better way to go about this simply because you have more control over the geometry:



And having more control means it will be a lot easier to optimize the model ( = Lower LI costs) , easier to create lower LoD models and Physics model later in the process.
So best to avoid Boolean cutting for SL :)